8371643: Remove ThreadLocalAllocBuffer::_reserve_for_allocation_prefetch

[albertnetymk]

Trivial removing obsoleted code for unsupported arch.

Test: tier1

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Progress

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Issue

• JDK-8371643: Remove ThreadLocalAllocBuffer::_reserve_for_allocation_prefetch (Enhancement - P4)

Reviewing

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[bridgekeeper]

👋 Welcome back ayang! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@albertnetymk The following label will be automatically applied to this pull request:

• hotspot

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[mlbridge]

Webrevs

• 01: Full - Incremental (0e447848)
• 00: Full (03330ac2)

[vnkozlov]

What happens if TLAB is at the end of heap page? Are you sure "prefetch" instructions on all OpenJDK platforms can touch unmapped memory? I see PPC can use AllocatePrefetchStyle == 3.

[vnkozlov]

Please ask all OpenJDK platforms supporters to test these changes.

Note, when this code was introduced we did not have so many platforms.

[vnkozlov]

You missed code in HS agent: src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/runtime/VM.java

[albertnetymk]

What happens if TLAB is at the end of heap page? Are you sure "prefetch" instructions on all OpenJDK platforms can touch unmapped memory? I see PPC can use AllocatePrefetchStyle == 3.

In every <arch>.ad file, there is // Must be safe to execute with invalid address (cannot fault) for prefetching.

I searched online that all currently supported platforms don't fault on prefetching invalid addresses.

[openjdk]

@albertnetymk serviceability has been added to this pull request based on files touched in new commit(s).